Hydraulic impulse turbine



June 20, 1933. P'FAU 1,914,926

HYDRAULIC IMPULSE TURBINE Filed Feb. 12. 1931 2 Sheets-Sheet 1 MAX/MUMbarn (1.. 4

NORMAL 7. W4.

June 20, 1933.

HYDRAULIC IMPULSE TURBINE PFAU 2 Sheets-Sheet 2 Filed Feb. 12. 1951Patented June 20, 1933 UNITED STATES PATENT QFFICE ARNOLD PIFAU, E.M'ILWAUKEE, WISCONSIN, ASSIGNOR TO ALLIS-CI-IAL1TEBS IVLANU- FACTURINGCOMPANY, 01? MILWAUKEE, WISCONSIN, A CORPORATION OF DELA- WEABEHYDRAULIC IMPULSE TURBINE Application filed February 12, 1931.

This invention relates in general to the art of hydraulic turbinesettings and relates more specifically to an impulse turbine setv tingfor sites subjected to tailw-ater elevations falling considerabledistances below normal level, and also rising some distances above thenormal tailwafter elevation.

An object of the invention is to provide an impulse turbine settingespecially well adapted for sites having the named tailwatercharacteristics, wherein a substantially constant discharge water level,as close to the normal tailrace elevation as is possible, is providedfor effecting the discharge of the hydraulic fluid from the submergeddischarge pit into the tailr-ace.

Another object of the invention is to provide an impulse turbine settingespecially v well adapted for sites having the named tailwatercharacteristics, wherein drowning of the buckets of the impulse wheel isellectively prevented.

It is 01 primary importance for successful and ellicient operation ofimpulse turbines that their buckets never become drowned in the tailwater. This applies to the vertical, as well as to the horizontal shafttype 01" impulse turbine, having one or more jets impinging upon thebuckets and having one or more runners on the shaft. lVhen the bucketsbecome submerged in the tailwater they collect water from it, whichcauses the wheel housing to become filled with water. This results in aconsiderable drop in the power developed by the wheel and therefore alsoin the efficiency thereof, and should be prevented. It has thereforebeen heretofore necessary to position the buckets a safe distance abovethe tailwater level to prevent said drowning or submergence of thebuckets.

It can be readily seen that for sites having substantially constanttailwater elevations,

that the distance, necessary between the tailwater elevation and thebuckets, to preclude drowning, is a minimum. That is, the headcorresponding to said distance, between the tailwater level and thecenterline of the nozzle or jet impinging upon the buckets, is aminimum.

In sites where the tailwater level rises Serial No. 515,268.

above and drops below the normal tailwa ter level, the wheels must bepositioned so that thebuckets thereof are spaced from the highesttailwater level. Acco1'dingly, tl1e wheel is positioned at a higherelevation than necessary for normal tailwater conditions of operation,which results in loss of head 011 the wheel, equivalent to the distancebetween the normal and said highest tailwater elevation. Then also whenthe tailwater level "drops below normal, an additional head on the wheelis lost, equivalent to the distance be tween this lower elevation andthe normal elevation of the tailwater.

To illustrate these losses in head, let us assume a site having a totalhead of 1000 feet and a maximum rise in tailwater elevation of feetabove the normal. This would amount to 1% of the total head or to a 1reduction in the output of the wheel. And if its maximum drop oftailwater elevation is feet below the normal, this loss in head is 2% ofthe total head, or a 3% output loss. So that the total loss of output,for flood level, or highest tailwater and lowest tailwater conditions ofoperation of the turbine is l constituting a material reduction in therevenue realizable on the turbine installation investment.

It is a more specific object of this invention ,to provide an impulseturbine setting with means for utilizing the additional head availablein sites subjected to tailwater elevations dropping substantialdistances below normal tailwater elevation, by creating asub-atmospheric pressure within the wheel housing, by reason of whichthe windage losses of the revolving buckets is also reduced and thusfurther enhancing the efiiciency of the turbine setting.

It is an additional specific object of this invention to provide animpulse turbine setting having a discharge pit, the discharge end ofwhich is constantly submerged by the .tailrace water even at the maximumlow tailwater elevation, with means for limiting the effect of the headmeasured between high and maximum high tailwater elevation ascontrolling the elevation of the discharge water in the discharge pit,whereby the detrimental efl'ect of said floor head on the wheel may beavoided and the buckets of the impulse wheel may be positioned adistance nearer the discharge level measured by said head limitation andstill not be drowned at maximum high tailwater elevation.

Fig. 1 is a transverse section of a hydraulic impulse turbine set-ting,capable of carrying out the objects of the invention stated in theparagraph next to the above.

Fig. 2 is a transverse section of a modified form of hydraulc impulseturbine setting, capable of carrying out the objects of the invention asis the setting shown in Fig. 1 and provided with means for additionallycarrying out the objects of the invention stated in said aboveparagraph.

Referring to the drawings on which 1 embodies an impuls: 'ne settingconstructed according to his invention, reiterence numeral 1 designatesgenerally the novel impulse turbine setting. This comprises a dischargepit 2 of rectangular or circular cross-section and being in controllablecommunication through a stop log gate 1%- with.

the tailrace 21. At its upper end the discharge pit 2 is provided withtransverse, auxiliary outlet 3, having a bounding, sill portion 22, toafford a direct outlet for the discharged water, at the upper end of thedischarge pit 2. when the setting is subjected to flood or hightailwater conditiors. The concrete material. portion 27 torn g the upperboundary of the auxiliary outlet 3, cooperates with the wheel housing 5,of suitable material, to withstand the maximum suction head, and theplate 23 supporting nozzle 6 to form a closed space for the wheel 12when the gate 4; contr lling the auxiliary out let 3 is in closedposition.

A pipe 10 communicates at one end with the interior of the wheel housing5. outside of the orbit of rotation of the peripheral portions of thebuckets 24, to admit air at at mospheric pressure into the housing. Thisair admission is controlled by means oi a siiding type of air valve 7 towhich the other end of pipe 10 is connected. The air valve 7 isregulated according to the love of the discharge water below the wheel12 by means of a float 8. free to rise and fall, to which the air valve7 is connected by a rigid stem 25, said stem being guided by brackets 9positioned within an opening provided in concrete material portion 27 toreceive the stem.

The gate 4 is guided in slots provided in the opposed side walls of theauxiliary outlet 3 and when in closed position its lower and upper endsare, respectively received Within a groove in sill portion and within analigned, transverse opening in concrete portion 27. The gate 4 isprovided with an operating rod 15 having an external screw thread in aportion of its length. This screw thread is engaged by the similarlythreaded rod-surrounding portion of a worm wheel 19 fixed for rotationwithin a housing held in spaced relation with respect to an electricdriving motor 17 having a. worm 18 on its shaft, which cooperates withthe worm wheel 19.

Having now described the essential elements of the novel impulw turbinesetting, the principle underlying the setting shown in Fig. 1 will nowbe explained. The figure shows the setting operating at normal tailwatercondition, the normal elevation being so designated on the figure. Themaximum high tailwater elevation also indicated on the figure is seen tobe a safe distance from the buckets of the wheel 12. The maximum lowtailwater elevation also indicated on the figure is of a suflicientvalue to constantly submerge the discharge end of the discharge pit 2.The head between this elevation and the normal elevation is designated hsince it is the maximum head that may be added to the head on the wheel,under conditions of operating the impulse wheel 12 at the said maximumlow tail-water elevation. Intermediate values of head It, may be gainedon the wheel 12 depending upon the particular intermediate values of lowtail water elevations below the normal elevation. The particular head Itso gained adds to the available head on the turbine wheel, therebyincreasing the discharge capacity and the output of the wheel. Saidheads being realized by creating a. subatmospheric pressure in thedischarge pit and wheel housing, so that the windage loss of therevolving buckets is correspondingly reduced to further enhanceefiiciency of the wheel. And as long as the tailwater level lies abovethe sill 22 of the auxiliary outlet 3 the gate 4 could be in openposition so that a. free outlet would be had, that is, the wheel housingwould be in open communication with the atmosphere as shown.

When the tailwat-er level drops a certain distance below normal to alevel. which renders it profitable to utilize the corresponding head,the float 8 also drops thereby accomplishing two things. First, it shutsoff the air supply to the wheel. housing. Secondly, it closes thecircuit of motor 17 in a direction such that the gate 4. is lowered toits closed position. The water discharged from the buckets 24- of thewheel 12 must now enter the tailrace 21 through the discharge pit 2.

The discharge of the water from the buck ots of an impulse wheel takesplace at a high Velocity. The said discharged water further carries airentrained from the air present within the wheel housing. In this mannerthe wheel housing becomes more and more devoid of air and the water inthe discharge pit 2 rises in consequence thereof. This rise of waterlevel in the discharge pit 2 would soon tend to submerge the buckets 24,a con dition to be avoided. Therefore, in order to prevent further risein said level and to in fact lower same, instrumentalities should beprovided to suppress or lower the said level. The drawings show airadmission means for efleoting this result. WVith the disclosed means thewater level in the discharge pit 2 can be held close to the value of thenormal tailwater elevation, and the distance between the low tailwaterelevation and the elevation of the water in the discharge pit 2represents the head it, so gained.

lVith both the tailrace 21 and the discharge pit 2 subjected toatmospheric air pressure there must be a higher level for the waterinthe discharge pit than the level of the water in the tailrace 21 in.order that a flow of the discharge water ensue through the dischargepit. Therefore, the water level in the discharge pit 2 when theauxiliary outlet 3 is closed will always be somewhat higher than thetailwater level by an amount which corresponds to the head necessary toeffect the flow of the said discharge water through the sealed dischargepit 2. Accordingly, if we now assume a rise in the tailwater level andsuch a rise to bring it up to or above its normal value, the level ofthe water in the still sealed discharge pit 2 would be above this normalvalue. The effect of this undesirable rise of the water in the dischargepit 2 is to cause the float 8 to rise and close the circuit of theelectric motor 17 in the reverse direction, to again raise the gate 4:,so as to restore a discharge from the discharge pit 2 through theauxiliary outlet 3.

Again referring to Fig. 1 of the drawings wherein is shown automaticallycontrol 1 means by which the principle just described and underlyingthis invention applied. the operation thereof will now be fuTydescribed. The figure it will be noted shows the im pulse turbinesetting 1 in open gate condition, the bucket discharged water passingdirectly into the tailrace 21 through auxiliary outlet 3, the gate lbeing fully open and the float 8 in approximately the mid-position ofits vertical range of movement. If the tail- Water level falls a certaindistance the switch actuating arm 11 on the air valve 7 will bepermitted by the float S to fall into engagement with switch 32 to closethe same. When the switch 32 is closed the air valve 7 will have beenmoved to closed position, in which no air can be admitted into the wheelhousing 5 through pipe 10, which clearly appears from the drawings.Also, since the gate 4 is still in open position in which the switchactuating arm 16 thereon engages the switch 44 and holds it in closedposi on, the upper relay switch 48 is in open pcs i the similar, lowerrelay switch 34 is in clo ed position which conditions must be satisfiedin order that the winding 35 be energized as soon as switch 32 is closedto cause it to close the motor switch t138. The circuits involved andthe last two closing in the or der stated are first, through switch 44;line 2830-43 i44546line 29. Second, through switch 32: line 283031323at-3536-line 29. Third, through motor switch el-38: line 28373839-17 4Ol152line 29. Energization of the circuit of motor 17 in the directionstated causes it to close the gate l. T he under pressure which underthis closed gate condition of the setting 1 is being created in thewheel housing 5 tends to bring the level of the water in the dischargepit 2, now sealed against the atmosphere, to the normal level of thetailwater, even though the tailwater level is low. The float 8 must thenrise to this level and in so doing raises the air valve 7 to its openposition and admitting air into the wheel housing 5 through pipe 10,thereby tending to restore atmospheric pressure in the discharge pit 2to which pressure water in the tailrace 21 is always subjected. Underthis condition the elevation of the water in the discharge pit 2 must beof a somewhat greater value than the particular low elevation of thetailwater, to provide the head necessary to effect a flow of the dischare water through the discharge pit 2.

Now, if the tailwater level rises to or beyond the normal level, thelevel in the dis charge pit 2 which has been maintained near thetailwater normal level, will rise a corresponding amount. Float 8 thenalso rises further to cause the switch arm 11 to engage and close switch50, air valve 7 being open during this time, to cause the air admittedthrough pipe 10 to suppress this rising level in the discharge pit. Theswitch 47 is at this time held closed by arm 16 on the gate rod 15,since the gate a is down or in closed position. This effects theci'iergization of the winding 42 to open relay switch 3% and todeenergize winding 46 to permit a gravity closing of the relay switch48. lVhen the switch 50 is then closed, a closed circuit through thewinding 49 is established to cause the switch 88-- 41 to close thecircuit to the motor 17 in the reverse direction to again raise the gateand restore the different elements of the setting to the positions inwhich they are shown 011 the drawing.

The circuits involved under the condition just stated and the last twoclosing in the order stated are first, through switch 47: line2830-43t7-4236line 29. Second, through switch 50: line 28303l-50514948line 29. Third, through motor switch 3841: line 28-37384c017-394c1-52line 29.

Now referring to Fig. 2 which shows a setting provided with means foralso adjusting the level in the submerged discharge pit for tailwaterelevations between high tailwater elevation and maximum high tailwaterelevation, reference numeral 61 designates the impulse turbine settinggenerally. 62 is a discharge pit with the outlet portion constructed inthe form of an aspirator for producing a suction utilized to extract theair from the wheel housing 75, the tapered draft tube or tailrace endportion 63 thereof being constantly submerged by the water in thetailrace 81, as is the discharge pit 2 of the setting shown in Fig. 1.The outlet portion of the discharge pit 62 has athroat portion 64 theWalls of which being provided with apertures, said apertures being incommunication with an aspirator chamber 65.

Located in the vertical wall portion 69 is a chamber 110 incommunication at its lower end with the discharge pit 62 through a passage 111 and in communication at its upper end with the wheel housing 75through a horizontal venting passage 115 terminating opposite adeflector plate 116. Positioned above the chamber 110 is a valve casing77, sealed from the chamber 110 by a stem-receiving, cover plate 114 anddivided by a partition 105 into an upper chamber 106 and a lower chamber107. The lower chamber 107 is in controllable communication only withthe interior of the wheel housing 75, through a pipe 109 and a commonpassage 108 formed in the valve casing 77 and with the aspirator chamber65 through a conduit 112. The chamber 110 contains a float 68 having arelatively long, rigid stem 85 extending through the valve casing 77 andterminating in a switch 79. The stem 85 is guided by the partition 105and by the cover plate 114 which are providedrwith openings.

to receive it. The means for controllingthe communication between theinterior of the wheel housing and the aspirator chamber 65 comprises asuction valve 73 having a seating portion 71 in the valvehousing 77. Thevalve 7 3 limited by a fixed collar 93 to a displacement relative to thestem in the seating direction, and is limited by a compression spring 74and an adjustable collar 78, to a displacement relative to the stem 85in the valve opening direction.

Located within the upper chamber 106 is a seating portion 70 for an airvalve 67 which seats in the downward direction, whereas the suctionvalve 7 3 already described seats in the reverse or upward direction.Valve 67 is similarly limited by a fixed collar 94 to a displacementrelative to the stem 85 in the seating direction and is limited. by acompression spring and an adjustable collar 96 to a displacementrelative to the stem 85 in the opening direction.

Chamber 106 is in communication at its lower end with the common passage108 and at its upper end is in controllable communication with theatmosphere through a check valve 86 having a seating portion 87 and aguide stem 89 which is supported and guided within a cage 88 extendingfrom the valve casing 77. The valve 86 is normally gently held in closedposition by a compression spring 90 the ends of which cooperate with thecage 88 and with an adjustable collar 91.

In order to at times be able to supply the wheel housing 75 withcompressed air the setting 61 is provided with a pair of power leads 97and 98 for supplying current to an electric motor 82 drivingly connectedto an air compressor 83. The discharge of the air compressor isconnected to a receiver 103 having a compressed air line 84 incontrollable communication with the chamber 106. This communication iscontrolled by a magnetically operated valve 102 having a winding 101 inseries with the cooperating contacts 80 of the switch 79. The circuit tothe motor 82 is controlled according to the pressure within the receiver103 by means of a pneumatically operated switch 104.

76 is a nozzle which directs a jet upon the buckets 99 of the wheel 72carried by a horizontal shaft 113. The shaft 113 may be horizontal asshown or vertical, and may carry one or more wheels 72 and each wheelmay have one or more jets impinging upon the buckets 99 thereof.

represents slots in the sine walls of the tailrace 81 for receiving stoplogs, isolating the discharge pit 62 from the pressure of the tailracewater to permit of ones gaining access to the discharge pit 6E2 at floodor maximum high tailwater elevation conditions of the setting.

The lines indicating maximum low tailwater, normal, high and maximumhigh tail-- water elevations in the tailracc 81 have been marked MLTJV,Nfllllh, HTJV. and ll*l.H.T.lV., respectively, on the drawings, whilethe lines indicating the discharge pit water elevations correspmidingrespectively, to these tailrace elevations have been marked mlzflm,ll-15.10., lair/.0. and mJatxux, respectively.

The operation of the form of hydraulic impulse turbine setting shown inFig. 2 is as fOllOWf T he figure shows the setting operating undernormal tailwater elevation conditions and the elevation of the dischargewater in the discharge pit is somewhat greater tl an the tailwaterelevation. and the chcclc valve 86, the air valve 67 and the suctionvalve 73 being closed. It the level within the discharge pit 62 causedto drop because of a drop in tailrace level, float 68 drops acorresponding amount and opens the suction valve 73 to establishcommunication between the wheel housing an d the aspirator chamber 65.The suction i i-"Feet produced in the chamber 65 by the high velocityflow of discharge water, transversely past the apertures 66 in the wallsof the draft tube portion 63 of the discharge pit 62, is accordinglycommunicated to the interior of the wheel housing 7 5 to extract airtherefrom and to place said wheel housing under sub-atmospheric pressurewhich action is, of course, somewhat augmented by the tendency of theimpulse turbine when in operation, to create a subatmospheric pressurewithin the sealed wheel housing, as explained in connection with thesetting shown in Fig. 1. The elevation of the discharge water in thedischarge pit 6:2 accordingly may rise because of the created suction toa value indicated by the line marked mliao. on the drawings which mayexist even with a maximum drop in tailwater level in the tailrace 8-1,to that indicated by the line marked M.L.T.l V., just sufiicient tosubmerge the discharge end of the discharge p The valves 67 and 73 arearranged so that the air valve 67 is ready to open when the suctionvalve 7 3 is seated, so that as the level of the water in the tailrace81 rises through the normal value toward the indicated high tail waterelevation the aspirator suction to the wheel housing is cut off by thesuction valve 73' and the level of the discharge water in the dischargepit rises a certain amount and continues to elevate the float 68, whichcauses the stem 85 thereof to open the air valve 67, to permit the checkvalve 86 to open to admit atmospheric air into the wheel housing 75,assumed to be for the time being under such moderate negative pressure,as to permit of the opening of check valve 86. hen the pressure withinthe wheel housing reaches approximately atmospheric pressure, checkvalve 86 may close and the elevation of the water in the tailrace 81when this event happens may be at the high tailwater elevation,indicated by the line marked HTIV. on the drawings, and the elevation ofthe discharge water in the discharge pit corresponding to said tailraceelevation may be as indicated by the line marked haw. on the drawings.And also as the said HTRV. elevation in the tailrace is reached thefloat 68 holds the stem 85 at an elevation at which the switch 79carried thereby bridges the contacts 80 to close the circuit to thewinding 101 of the electromagnetically controlled valve 102' to opensame and admit air at a desired overpressure from the reservoir 103,into the wheel housing 75, through the air line 84, past the open airvalve 67 and the connecting pipe 109. i th this pressure air admissionthe elevation of the discharge water in the discharge pit 62 may belimited to a value as indicated by the line marked mihjcw. when theelevation of the water in the tailrace stands at its maximum high value,indicated by the line marked M.H.T.V. on the drawings. It is, of course,not desirable to admit more compressed air into the wheel housing 75than necessary for the particular maximum high tailwater elevation towhich the setting is subjected. The compressed air provides theadditional head necessary to force the discharge water from the wheelthrough the submerged dischar e pit to the outside and even against themaximum high tailwater. This back pressure reduces the head at the:nozzle or jet resulting in a loss of output and also increases thewindage losses of the buckets at high tailwater conditions of operationof the setting. It, however, p vents drowning of the wheel which wouldrc r in a much greater loss of output and o. einciency, and it permitsof utilizing the full head at nor; and, partly at least, at lo Ytailwater conditions of operation of the setting. The discharge pitwater elevation may with this form of setting be maintained as close tothe normal elevation, as possible, under conditions of maximum hightailwater elevati(in-operation, as well as, under maximum low tailwaterconditions of operation of the setting. It therefore is applicable forsites having a greater variation between maximum low and the maximumhigh tailwater elevation than is the case with the setting shown in Fig.1.

It will be seen that the setting arrangement shown in Fig. 2 takes careof the requirements fulfilled by the setting shown in Fig. 1, but itwould be unnecessarily complicated to warrant its use at sites where noextreme flood tailwater elevations are involved. And it may be herenoted that, ordinarily it would not be necessary to introduce thecompressed air supply means, if the flood elevation or the maximum hightailwater elevation is less than, say feet above the maximum lowtailwater elevation.

It should be understood that it is not desired to limit the invention tothe exact details of construction shown and described, for obviousmodifications may occur to persons skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. In a hydraulic impulse turbine setting, a wheel housing, a tailrace,a discharge pit in communication with said wheel housing and beingsealed from the outside by the water in said tailrace, an auxiliaryoutlet for discharged water, in communication with said wheel housingand with said. discharge pit, a gate for controlling said auxiliaryoutlet, and means responsive to the changes in level of the dischargewater for operating said gate.

2. In a hydraulic impulse turbine setting, a wheel housing, a tailrace,a discharge pit in communication with said wheel housing, an auxiliaryoutlet for discharged water, in communication with said wheel housingsaid tail race and with said discharge pit, and means for closing saidauxiliary outlet, said discharge pit being sealed by the water in thetailrace from the atmosphere when said auxiliary outlet is closed.

lib

3. In a hydraulic impulse turbine setting for sites having tailwaterlevels dropping considerably below the normal level, a wheel housing, awheel in said housing, a tailrace, a discharge pit submerged by thetailrace water and forming a passage for the water discharged from saidwheel, and an auxiliary outlet for said discharged water and being incommunication with said wheel housing.

4. In a hydraulic impulse turbine setting for sites having tailwaterlevels dropping below the normal level, a tailrace, a wheel housing, awheel having peripheral buckets, fixed for rotation within said housing,a discharge pit in communication with said wheel housing and sealedagainst the atmosphere by the water in said tailrace, an auxiliaryoutlet for discharged water, in communication with said wheel housingand being normally in communication with the tailrace and the atmosphereand means for maintaining a substantially constant distance between saidbuckets and the adjacent discharge water level.

5. In a hydraulic impulse turbine setting for sites having tailwaterlevels dropping below the normal level, a tailrace, a wheel housing, adischarge pit in communication with said wheel housing, a portionthereof being continuously submerged by the water in said tailrace, anauxiliary outlet for discharged water, in communication with said wheelhousing and with said discharge pit, said discharge pit being in opencommunication with normal elevation tailwater through said outlet, andmeans connected with said discharge pit for maintaining a column ofwater in said discharge pit whose elevation conforms closely to thenormal ta ilwater elevation.

6. In a hydraulic impulse turbine setting for sites having tailwaterlevels dropping below the normal level, a tailrace, a wheel housing, adischarge pit in communication with said wheel housing and sealedagainst the atmosphere by the water in said tailrace, an auxiliaryoutlet for discharged water, in communication with said wheel housingand being normally in communication with the tailrace and theatmosphere, and means connected with said auxiliary outlet and saidwheel housing for maintaining a substantially constant level of thewater in said discharge pit.

7. In a hydraulic impulse turbine setting for sites having tailwaterlevels falling below the normal level, a wheel housing, a discharge pitin communication with said wheel housing, a tailrace, a portion of saiddischarge pit being continuously submerged by the water in saidtailrace, an auxiliary outlet for discharged water, in communicationwith said wheel housing said tailrace and with said discharge pit, andmeans for closing said auxiliary outlet when the tailwater level fallsbelow the normal level.

8. In a hydraulc impulse turbine setting for sites having tailwaterlevels falling below the normal level, a wheel housing, an im- 7 pulsewheel positioned within said housing, a discharge pit in communicationwith said wheel housing, a tailrace, a portion of said discharge pitbeing constantly submerged by the water in said tailrace, an auxiliaryoutlet in direct communication with said wheel housing and with saidtailrace, said auxiliary outlet being closed when the tailwater levelfalls below normal, and means for opening said auxiliary outlet toestabwheel housing, a tailrace, a. portion of said discharge pit beingconstantly submerged by the water in said tailrace, an auxiliary outletin direct communication with said wheel housing and with said tailrace,said auxiliary outlet being closed when the tailwater level falls belownormal, means for opening said auxiliary outlet to establish a dischargeof water discharged from the wheel of said wheel housing through saidoutlet when the tailwater subsequently rises to above normal elevation,and means connected with said means for admitting air into the wheelhousing while the tailwater level is so rising.

10. In a hydraulic impulse turbine setting, a wheel housing, an impulsewheel positioned within said housing, a tailrace, a discharge pit incommunication with said wheel housing and having its discharge endcontinuously submerged by the water in said tailrace, and an aspiratorchamber connected with said discharge pit and being in controllablecommunication with the interior of said wheel housing, said aspiratorchamber being actuated by the water flowing through said discharge pitand serving when its controllable communication with the wheel housingis open to withdraw air from the interior of said wheel housing.

11. In a hydraulic impulse turbine setting for sites having tailwaterlevels rising above and falling below the normal level, a tailrace, asingle chamber wheel housing, an impulse wheel positioned within saidhousing, a dis charge pit in communication with said wheel housing andbeing sealed against the atmosphere under normal tailwaterelevation-coudition of operation of the setting, means connected withand cooperating directly with said discharge pit, and means includingsaid means for maintaining a substantially constant level of the waterin said discharge pit, notwithstanding rises and falls of the level ofthe tailwater from its normal level.

12. In a hydraulic impulse turbine setting for sites having tailwaterlevels rising above and tailing below the normal level, a tailrace, asingle chamber wheel housing, an impulse wheel positioned within saidhousing, a discharge pit in communication with said wheel housing, thedischarge end thereof being continuously submerged by the water in saidtailrace, said discharge pit being sealed against the atmosphere undernormal tailwater elevation condition of operation of the setting, meansconnected with and cooperating directly with said discharge pit, andmeans including said means for adjusting the pressure within said wheelhousing in accordance with the tailwater levels, above and below thenormal level.

13. In a hydraulic impulse turbine setting for sites having tailwaterlevels dropping considerably below the normal level, a wheel housing, animpulse wheel positioned within said housing, a tailrace, a dischargepit in communication with said wheel housing, the discharge end thereofbeing continuously submerged by the water in the tailrace, suction meansassociated with said discharge pit, said means being in controllablecommunication only with the interior of said wheel hous ing, and meansresponsive to changes in level of the discharge water in the dischargepit for controlling said communication, said suction means beingactuated by the water discharged from said wheel and flowing throughsaid discharge pit.

14. In a hydraulic impulse turbine setting for sites having tailwaterelevations varying from the normal elevation, a single chamber wheel.housing, an impulse wheel positioned within said housing, a tailrace, adischarge pit in communication with said wheel housing, the dischargeend thereof being continuously submerged by the water in said tailrace,means permitting evacuation of the air within said wheel housing whenthetailwater level falls below normal and means for permitting admission ofatmospheric air into said wheel housing when the tailwater levelsubsequently rises above the normal level.

15. In a hydraulic impulse turbine setting for sites having tailwaterelevations varying from the normal elevation, a single chamber wheelhousing, an impulse wheel positioned within said housing, a tailrace, adischarge pit in communication with the wheel housing, the discharge endthereof being continuously submerged by the water in said tailrace,means for eii'ecting evacuation of the air within said wheel housingwhen the tailwater level falls below normal, and means for admittingcompressed air to said wheel housing when the tailwater level has risenabove the normal level.

16. In a hydraulic impulse turbine setting for sites having tailwaterelevations varying from the normal elevation, a single chamber wheelhousing, an impulse wheel positioned within said housing, a tailrace, adischarge pit in communication with the wheel housing, the discharge endthereof being continuously submerged by the water in said tailrace, saiddischarge pit being sealed against the atmosphere under normal tailwaterelevation-condition of operation of the setting, means for effectingevacuation of the air with in said wheel housing when the tailwaterlevel falls below normal, and means for admitting compressed air to saidwheel housing when the tailwater level has risen above the normal level.

In testimony whereof, the signature of the inventor is affixed hereto.

ARNOLD PFAU.

